1. Field of the Invention
The present invention relates generally to measurement of the Frankfort Mandibular Plane Angle (FMA) and more specifically to the non-invasive, external measurement of FMA, without x-ray.
2. Description of the Background Art
The Frankfurt Mandibular Plane Angle is defined as the angle formed by the intersection of two extended lines: one drawn through the gonion and the second through the porion and orbitale. Traditionally, the FMA is determined by utilizing a lateral cephalometric radiograph, which is developed in an x-ray film processor, dried, labeled and then covered by an acetate sheet. The landmarks are marked, lines traced, and the FMA measured with a protractor. Most recently, charged coupled devices are irradiated in a similar fashion to the lateral cephalogram and the resultant image digitized. The FMA is then determined with the aid of a computer software program after the landmarks are identified. The major limitations and disadvantages of both of these techniques are that invasive x-rays irradiate most of the patient""s head, and very costly, cumbersome equipment is required. Also, a skilled dentist, radiologist, or highly trained technician, who has had long experience in tracing these radiographs, must spend time discerning indistinct landmarks, tracing on the acetate coversheet, and xe2x80x9cestimatingxe2x80x9d the FMA with a protractor. Specially shielded x-ray rooms are required when exposing dental x-rays, costly developing machines, and dangerous and harmful chemicals are required. Retakes of the x-ray must be done if the patient moves during exposure or if the head position or degree of mouth opening is not ideal.
It is an object of the present invention to measure a patient""s FMA without invasive procedures and without x-ray.
It is another object of the present invention to measure a patient""s FMA without x-rays.
It a further object of the present invention to measure a patient""s FMA without expensive special equipment.
These and other objects are achieved by a device that includes a frame having an upper bar and a downward bar extending from the upper bar at a known angle. The upper bar, when fitted to the patient, extends parallel to the patient""s porion-orbitale line. The rear bar is fixed to the upper bar extends from the patient""s porion to the patient""s gonion. A lower bar is movably attached to the rear bar and, when fitted to the patient, extends parallel to and at the same height as the patient""s gonion-menton line. Because the relationship between the fixed points of the bars and the fixed points of reference on the patient (porion, orbitale, gonion, and menton) and the dimensions and angular relationships between the various parts of the FMA gauge""s frame are known, the FMA can be determined by reading a measuring device on the gauge. In some embodiments, this angular determination can be made directly from the measuring device. In other embodiments, the measuring device indicates the position of the lower bar, once adjusted to the patient, with respect to the downward bar. This relative position may then be correlated with the patient""s FMA.